A note on “20th Century Boys”…
I don't quite know if you'd consider this a spoiler for 20th Century Boys, but...
They say it's dangerous, when writing about creative people, of actually showing what they create. If your representation isn't strong enough, it harms the credibility of the characters in a way that's pretty difficult to reverse.
Personally, I do like the song. One of the reasons I don't do music crit here on the site or elsewhere--or, at least, do very little of it--is because I know shit about music, my tastes are somewhat arbitrary, and I don't have the same complex set of standards that I apply to other media that I enjoy, comics or movies or whatever. But I enjoy it, a lot, really, tapping my foot etc.
But, is this the song that will save humanity? Man, Hell if I know. I just know that Urasawa inherently ran a bit of a risk by making the song available to his manga-reading audience. It's a little ballsy of him, and it seems to have largely paid off, near as I can tell, in Japan (I haven't seen the films yet--we have the first on DVD here at home, but we haven't yet had time to sit down with it).
Bryan Lee O'Malley's songs as "Kupek" (which I also like, dammit) do not appear to be the soundtrack of the upcoming film for Scott Pilgrim, at least from what I can tell from interviews. He clearly has had some influence--there was talk of Beck doing versions of the songs that appear in the books?--but O'Malley has also said that Sex Bob-Omb has a different musical style than he usually employs. It's a safer bet, because while I enjoy Kupek, not everyone does (O'Malley also benefits from characterizing Scott and his band as being not that good). He doesn't run the risk of his story hinging upon music that he'd written--music that might not go over as well with everyone.
20th Century Boys is enjoying a lot of critical success right now, but the English translation has a whole Hell of a long way to go. I do wonder if American audiences will respond to the climax's hinging upon this song in the same way that the Japanese audience did. You have admire his conviction, at any rate.